Thermal imaging and carbon isotope composition indicate variation amongst strawberry (Fragaria×ananassa) cultivars in stomatal conductance and water use efficiency

Abstract Cultivars with low stomatal conductance (gs) may show high water use efficiency (WUE) under drought conditions, but under optimal conditions low gs may result in low vigour. A combination of thermal imaging and carbon isotope composition (δ13C) analysis offers potential for screening simultaneously for both high gs and high WUE. Ten cultivars of strawberry (Fragaria × ananassa Duch.) were grown in well watered or water limited conditions. Thermal images were taken of the plants, with various approaches to determine the optimal protocol for detecting variation in gs, including use of reference leaves, grids to maintain leaves horizontal, and collection of meteorological data in synchrony with thermal images. δ13C of leaves, fruit, and crowns was determined. An index of gs derived from the temperature of horizontal leaves and the temperature of wet and dry references showed significant differences between cultivars and between well watered and water limited plants, as did gs estimated from leaf temperature, the temperature of a dry reference, and humidity. Thermal imaging indicated low gs in ‘Elsanta’ and ‘Totem’ and relatively high gs in well watered ‘Elvira’, ‘Florence’ and ‘Cambridge Favourite’. δ13C of all plant material was higher in water limited than well watered plants and showed significant differences between cultivars. In one experiment leaf δ13C indicated lowest WUE in ‘Elvira’ and highest WUE in ‘Totem’. δ13C was inversely correlated with an index of gs derived from thermal imaging. Although the results indicate substantial variation in gs and WUE between cultivars, generally all cultivars responded to water deficit by lowering gs and hence increasing WUE.